It is known in the engine art to provide cylinders with air intake ports through which charging and scavenging air is supplied to the engine combustion chambers, the ports being controlled by the reciprocating movement of the pistons and their associated piston rings within the cylinders during operation of the engine. It is also common to supply lubricating oil to the lower walls of the cylinders for lubrication of the sliding motion of the piston skirt and rings on the cylinder walls. During the reciprocating motion, in spite of the provision of oil control rings near the lower edge of the piston skirt, some small amount of lubricating oil will be continually displaced from the cylinder wall and piston surfaces into the cylinder intake ports. This oil may subsequently be picked up by the incoming charging and scavenging air and carried into the engine combustion chamber. Here some is burned in the normal combustion process and its residual products discharged to the engine exhaust system, while the remainder passes directly to the engine exhaust during scavenging of the cylinder with the fresh air charge.
In all engine arrangements, the result is an undesired loss of lubricants oil and a possible increase in engine combustion chamber deposits and/or exhaust emissions. If the engine is fitted with an emission control device, such as a catalytic converter, the additives found in engine lubricating oil may have a deleterious effect on the converter catalyst itself. Thus it is desired to improve control of the passage of lubricating oil into the engine combustion chambers and exhaust system to the extent possible, consistent with the necessity to provide lubrication for the reciprocating components.